From 519863ecab4db26d33d9a4af8f5284acf4b5ca29 Mon Sep 17 00:00:00 2001
From: Lucas Molas <schomatis@gmail.com>
Date: Wed, 5 Jan 2022 11:25:30 -0300
Subject: [PATCH] fix(core/node): unwrap fx error in node construction

---
 cmd/ipfs/daemon.go |  1 -
 core/builder.go    | 50 ++++++++++++++++++++++++++++++++++++++++++++--
 go.mod             |  1 +
 go.sum             |  3 ++-
 4 files changed, 51 insertions(+), 4 deletions(-)

diff --git a/cmd/ipfs/daemon.go b/cmd/ipfs/daemon.go
index a2c65b5b99e..7bf79426542 100644
--- a/cmd/ipfs/daemon.go
+++ b/cmd/ipfs/daemon.go
@@ -427,7 +427,6 @@ func daemonFunc(req *cmds.Request, re cmds.ResponseEmitter, env cmds.Environment
 
 	node, err := core.NewNode(req.Context, ncfg)
 	if err != nil {
-		log.Error("error from node construction: ", err)
 		return err
 	}
 	node.IsDaemon = true
diff --git a/core/builder.go b/core/builder.go
index e93ceddb2e3..c6bb9919206 100644
--- a/core/builder.go
+++ b/core/builder.go
@@ -2,6 +2,8 @@ package core
 
 import (
 	"context"
+	"fmt"
+	"reflect"
 	"sync"
 	"time"
 
@@ -9,6 +11,7 @@ import (
 	"github.com/ipfs/go-ipfs/core/node"
 
 	"github.com/ipfs/go-metrics-interface"
+	"go.uber.org/dig"
 	"go.uber.org/fx"
 )
 
@@ -75,11 +78,11 @@ func NewNode(ctx context.Context, cfg *BuildCfg) (*IpfsNode, error) {
 	}()
 
 	if app.Err() != nil {
-		return nil, app.Err()
+		return nil, logAndUnwrapFxError(app.Err())
 	}
 
 	if err := app.Start(ctx); err != nil {
-		return nil, err
+		return nil, logAndUnwrapFxError(err)
 	}
 
 	// TODO: How soon will bootstrap move to libp2p?
@@ -89,3 +92,46 @@ func NewNode(ctx context.Context, cfg *BuildCfg) (*IpfsNode, error) {
 
 	return n, n.Bootstrap(bootstrap.DefaultBootstrapConfig)
 }
+
+// Log the entire `app.Err()` but return only the innermost one to the user
+// given the full error can be very long (as it can expose the entire build
+// graph in a single string).
+//
+// The fx.App error exposed through `app.Err()` normally contains un-exported
+// errors from its low-level `dig` package:
+// * https://github.com/uber-go/dig/blob/5e5a20d/error.go#L82
+// These usually wrap themselves in many layers to expose where in the build
+// chain did the error happen. Although useful for a developer that needs to
+// debug it, it can be very confusing for a user that just wants the IPFS error
+// that he can probably fix without being aware of the entire chain.
+// Unwrapping everything is not the best solution as there can be useful
+// information in the intermediate errors, mainly in the next to last error
+// that locates which component is the build error coming from, but it's the
+// best we can do at the moment given all errors in dig are private and we
+// just have the generic `RootCause` API.
+func logAndUnwrapFxError(fxAppErr error) error {
+	if fxAppErr == nil {
+		return nil
+	}
+
+	log.Error("constructing the node: ", fxAppErr)
+
+	err := fxAppErr
+	for {
+		extractedErr := dig.RootCause(err)
+		// Note that the `RootCause` name is misleading as it just unwraps only
+		// *one* error layer at a time, so we need to continuously call it.
+		if !reflect.TypeOf(extractedErr).Comparable() {
+			// Some internal errors are not comparable (e.g., `dig.errMissingTypes`
+			// which is a slice) and we can't go further.
+			break
+		}
+		if extractedErr == err {
+			// We didn't unwrap any new error in the last call, reached the innermost one.
+			break
+		}
+		err = extractedErr
+	}
+
+	return fmt.Errorf("constructing the node (see log for full detail): %w", err)
+}
diff --git a/go.mod b/go.mod
index af332571d8c..6dbb86e3a15 100644
--- a/go.mod
+++ b/go.mod
@@ -104,6 +104,7 @@ require (
 	github.com/whyrusleeping/go-sysinfo v0.0.0-20190219211824-4a357d4b90b1
 	github.com/whyrusleeping/multiaddr-filter v0.0.0-20160516205228-e903e4adabd7
 	go.opencensus.io v0.23.0
+	go.uber.org/dig v1.14.0
 	go.uber.org/fx v1.16.0
 	go.uber.org/zap v1.21.0
 	golang.org/x/crypto v0.0.0-20210921155107-089bfa567519
diff --git a/go.sum b/go.sum
index 49abc3cac6d..e874965cbc0 100644
--- a/go.sum
+++ b/go.sum
@@ -1418,8 +1418,9 @@ go.uber.org/atomic v1.6.0/go.mod h1:sABNBOSYdrvTF6hTgEIbc7YasKWGhgEQZyfxyTvoXHQ=
 go.uber.org/atomic v1.7.0/go.mod h1:fEN4uk6kAWBTFdckzkM89CLk9XfWZrxpCo0nPH17wJc=
 go.uber.org/atomic v1.9.0 h1:ECmE8Bn/WFTYwEW/bpKD3M8VtR/zQVbavAoalC1PYyE=
 go.uber.org/atomic v1.9.0/go.mod h1:fEN4uk6kAWBTFdckzkM89CLk9XfWZrxpCo0nPH17wJc=
-go.uber.org/dig v1.12.0 h1:l1GQeZpEbss0/M4l/ZotuBndCrkMdjnygzgcuOjAdaY=
 go.uber.org/dig v1.12.0/go.mod h1:X34SnWGr8Fyla9zQNO2GSO2D+TIuqB14OS8JhYocIyw=
+go.uber.org/dig v1.14.0 h1:VmGvIH45/aapXPQkaOrK5u4B5B7jxZB98HM/utx0eME=
+go.uber.org/dig v1.14.0/go.mod h1:jHAn/z1Ld1luVVyGKOAIFYz/uBFqKjjEEdIqVAqfQ2o=
 go.uber.org/fx v1.16.0 h1:N8i80+X1DCX+qMRiKzM+jPPZiIiyK/bVCysga3+B+1w=
 go.uber.org/fx v1.16.0/go.mod h1:OMoT5BnXcOaiexlpjtpE4vcAmzyDKyRs9TRYXCzamx8=
 go.uber.org/goleak v1.0.0/go.mod h1:8a7PlsEVH3e/a/GLqe5IIrQx6GzcnRmZEufDUTk4A7A=